1. Field of the Invention
The present invention relates to use of stable, homogeneous slurries of particulate material and more particularly to a slurry of soil neutralizing material.
2. Description of the Prior Art
Agricultural lime such as calcium carbonate and dolomitic lime are normally applied as dry powders to sweeten or raise the pH level of soils in lawns, gardens and on farms. The lime products are prepared by grinding dolomitic lime, calcite or limestone to a variety of particle sizes or by using waste or by-products from other operations in the preparation of burnt lime, roadstone, chemical hydrate or other calcium-containing products. Particle sizes can vary from finer than 20 mesh (20/up) to finer than 100 mesh (100/up).
Application of these powdered materials in a dry state presented several well-known difficulties including uneven distribution and drifting of undesirable dust which is irritating and potentially dangerous to both humans and animals.
One proposed solution to these problems was to apply the lime as an aqueous slurry. Use of an aqueous lime slurry had many inherent advantages such as lower bulk, possibilities of much more even distribution, absence of dust, a degree of adhesion and adaptable to the simultaneous uniform application of other material.
The proposed aqueous lime slurry failed because of several reasons. Firstly, only unacceptably low lime concentrations could be prepared, because the rheological characteristics of undispersed limestone resulted in slurries that were difficult to pump and spray. Secondly, settling of the larger particle size components during make-down, storage handling or spraying further reduced the concentration and the settled material usually blocked the sprayer passages.
Attempts were made to increase the lime concentration by adding a dispersant such as tetrasodium pyrophosphate (TSPP), sodium tripolyphosphate (STP) or organic dispersants to lime slurries. The use of the dispersant allowed an increase in the concentration of particulate lime; however, it also increased the settling rate of the lime and resulted in failure since most of the lime would settle out within 15 minutes.